Closed hollow profiles, which have cross-sections and material thicknesses specially adapted to the application are increasingly being used in motor vehicles. Closed hollow profiles were previously generally produced in that firstly a tube is formed, the tube is subjected to corresponding bending and pre-forming processes and then a hydro-forming of the pre-bent or pre-formed tube into the final shape of the closed hollow profile takes place. On the one hand, not all components can be produced in this manner as in hydro-forming local elongations of the material are exceeded and thus cracks may form. In addition, there may be a non-manageable formation of folds during the hydro-forming. Moreover, the method steps previously used to produce a closed hollow profile adapted to the application are very complex and therefore expensive. A closed hollow profile may, in principle, also be produced from two deep-drawn half shells. During the deep-drawing of a blank, stresses are, however, introduced into the blank and lead to a spring-back of the half shell. The spring-back of the half shells makes the precise positioning of the half shells in a bottom die for welding the half shells into a closed hollow profile more difficult.
Assembling half shells which spring back strongly in a vehicle structure is very complex, however, because of the strong distortion. These parts alternatively have to be straightened and this entails very high costs.
A method for press-forming half shells, which are then welded to form a closed hollow profile, is known from the published European patent application EP 1 792 671 A1. The object of the European patent application mentioned is to provide half shells with thickened edge regions between the base region and the body. For this reason, a pre-formed half shell is firstly produced from a blank which provides excess material which is pressed during shaping into the final form from the base region into the edge regions between the body and the base region of the half shell. In comparison, the present invention deals with reducing the spring-back of deep-drawn half shells.